Process for producing a ca-ba-al-si-containing alloy

ABSTRACT

THIS INVENTION RELATES TO A CONTINUOUS PROCESS AND APPARATUS FOR PRODUCING A STEEL TREATING AGENT OF A CA-BA-ALSI-CONTAINING ALLOY AND PARTICULARLY TO AN INTERMEDIATE PRECHILLING STEP WHEREBY THE SLAG FROM A MOLTEN CA-BA-SI-CONTAINING ALLOY IS EFFECTIVELY REMOVED PRIOR TO INTRODUCING THE ADDITIVES OF ALUMINUM AND A METAL SELECTED FROM THE GROUP CONSISTNG OF IRON, NICKEL, CHROMIUM, COBALT AND MAGANESE, TO FORM THE CA-BA-AL-SI-CONTAINING ALLOY.   D R A W I N G

May 22, 1973 5, KQZAK ET AL 3,734,714

PROCESS FOR PRODUCING A (h-B. Al-Si-CON'IAININU ALLOY Filed Sept. 29,1970 mvmams Emma Kwmk 0mm P MW/er AWOYRNEEY United States Patent Office3,734,714 PROCESS FOR PRODUCING A Ca-Ba-Al-Si- CONTAINING ALLOY DonaldS. Kozak, North Tonawanda, N.Y., and David P.

Miller, Marietta, Ohio, assignors to Union Carbide Corporation, NewYork, NY.

Filed Sept. 29, 1970, Ser. No. 76,466 Int. Cl. C22d 7/06 U.S. Cl. 75-10R 9 Claims ABSTRACT OF THE DISCLOSURE This invention relates to acontinuous process and apparatus for producing a steel treating agent ofa Ca-Ba-Al- Si-containing alloy and particularly to an intermediateprechilling step whereby the slag from a molten Ca-Ba-Si-containingalloy is effectively removed prior to introducing the additives ofaluminum and a metal selected from the group consisting of iron, nickel,chromium, cobalt and manganese, to form the Ca-Ba-Al-Si-containingalloy.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to a continuous process and apparatus for producing aCa-Ba-Al-Si-containing alloy which can be used as a deoxidizing andcleansing agent to retard the formation of residual inclusions in highquality steels. More particularly, the present invention is directed toan intermediate prechilling step for effectively and economicallyremoving the slag from a conventionally prepared moltenCa-Ba-Si-containing alloy prior to introducing the additives of aluminumand a metal, such as iron, to form a Ca-Ba-Al-Si-containing alloy.

Description of the prior art Acalcium-barium-aluminum-silicon-containing alloy is presently being usedas an addition agent for treating steels. This aluminum-containing agentretards the formation of residual inclusions in high quality steels thusmaking the steels usable for precision fabricated parts such as ballbearings and the like. The usual technique for producing this additionagent is to initially prepare, in a submerged arc furnace, an alloyconsisting essentially of about 13 to 20% calcium, about 55 to 65%silicon, about 13 to 20% barium and up to iron and/or aluminum.

In preparing this Ca-Ba-Si-containing alloy from commercially availablecharges of these elements, a slag composed essentially ofcalcium-barium-silicate and having approximately the same density as thealloy at the tapping temperature of the arc furnace, which is about 250lbs/ft. at about 1800 C., is intermixed with the alloy. Thiscontaminated alloy is in a state not amenable for the acceptance ofadditional charges of aluminum and a metal to produce an overallchemistry which renders the alloy suitable for use as an agent fortreating steels. The closeness of the densities between thisCa-Ba-Si-containing alloy and the slag makes impractical theconventional skimming and back-pouring techniques usually employed forseparating slag from .molten metals. Consequently it is necessary tocool or freeze the slag and Ca-Ba-Si-containing alloy mixture in chillsor the like, whereupon during the initial cooling period the slagbecomes more viscous than the alloy and settles to the bottom of thechills. Thereafter the slag layer is mechanically or manually removed byconventional means and the Ca-Ba-Si-containing alloy layer is thencrushed into small sizes. The sized alloy is next fed into a furnace,such as an induction furnace, where it is heated to a temperature ofabout 1150 C. Additives of aluminum and a metal such as iron are thenPatented May 22, 1973 introduced in precalculated amounts, with orwithout additional fines of a Ba-Ca-Si-containing alloy, so as toregulate the chemistry of the overall composite to produce an alloyconsisting essentially of about 17-24% aluminum, about 37-43% silicon,about 8l3% barium, about 9- 14% calcium, and up to about 25% of at leastone metal selected from a group consisting of iron, manganese, nickel,chromium and cobalt; preferably iron.

The Ca-Ba-Al-Si-containing alloys is then tapped into chills or the likewhere it solidifies, after which it is crushed by conventionaltechniques into usable sizes.

The separate handling of the Ca-Ba-Si-containing alloy along with theexpense of operating a furnace to remelt it increases the overall costof producing this steel treating agent.

It is the object of this invention to provide a process for separatingthe slag from the Ca-Ba-Si-containing alloy while the mixture is stillin the .molten state so that the aluminum and metal additives can beincorporated directly into the molten Ca-Ba-Si-containing alloy therebyavoiding the necessity and expense of a separate remelt step asdescribed above.

SUMMARY OF THE INVENTION This invention relates to a continuous processand apparatus for economically producing a steel treating agent of aCa-Ba-Al-Si-containing alloy consisting essentially of about 8-13%barium, about 914'% calcium, about 17- ?A% aluminum, about 37-43%silicon and up to about 25 of at least one metal selected from a :groupconsisting of iron, nickel, chromium, cobalt and manganese. A Ca-Ba-Sialloy containing about 13-20% calcium, about 1320% barium, about 55-65%silicon and up to 10% iron and/ or aluminum is initially produced in asubmerged arc furnace by conventional techniques using commerciallyavailable charges of these elements. The Ca-Ba-Si-containing alloyintermixed with slag is tapped from the furnace at a temperature ofbetween about 1500 C. and about 2100 (1., preferably about 1800 C. Sinceapproximate equality of the densities of the slag and the alloy preventsconventional separation therebetween at this temperature, the moltencomposite is tapped onto a downwardly inclined prechill runner composedof a refractory material such as sand, brick, graphite or the like. Therunner consists of an initially straight segment followed by a secondsegment containing at least one barrier or projection in the path of theflow to trap, by dam-like means, a portion of the molten composite. Theinitially straight segment of the runner is designed to permit thecooling of the tapped molten alloy and slag composite to between about1150 C. and about 1700 C. from the tap temperature which is about 1800C. Within this temperature range, the slag component of the gravityflowing composite becomes more viscous than the alloy and begins tosettle to the bottom of the flow while the alloy rises to the surface.Upon reaching the first barrier, the gravity flow of the compositeencounters its first obstacle in which a portion of the lower or bottomlayer of the composite containing the slag is trapped while the upper ortop layer of the composite, containing substantially the alloy,continues to flow over the barrier. The height of the barrier iscalculated so as to trap the slag while providing little or no impedanceto the flow of the top layer of the composite containing theCa-Ba-Sicontaining alloy.

To increase the degree of separation between the slag and alloycomponents, additional barriers may be provided in the path of the flowuntil a predetermined grade of purity of the Ca-Ba-Si-containing alloyis obtained.

The temperature, however, can not be permitted to get The degree ofincline of the prechill runner is variable and depends on the length ofthe initially straight segment of the runner and the height of thebarrier or barriers on the second segment. For example, a shortinitially straight segment for the runner will require a slope which isless than that required for a longer length straight segment since thetapped molten composite will have to be cooled to a degree necessary tohave the slag become more viscous than the alloy. Likewise, the heightof the barriers also influences the degree of slope of the runner sinceif the barrier is too low and the slope is high, the slag will not betrapped. The criticality of the runner with respect to length, slope andthe height of the barriers thereon is that they be adjusted so thatduring the initial flow of the tapped molten composite, the cooling ofthe composite will be sufiicient to allow the slag component to becomemore viscous thereby enabling the first and possible subsequent barrierto effectively trap the slag.

The relatively pure Ca-Ba-Si-containing alloy at the end of the runneris fed into a preheated insulated ladle at a temperature between about1150 C. and about 1700 C., preferably about 1300 C., where it is thenweighed. The required amount of aluminum and a metal, such as iron,necessary to adjust the chemistry of the alloy to the range given aboveis calculated and then added to the ladle. In some cases fines of aCa-Ba,Si-containing alloy and/or a Ba-Ca-Al-Si-containing alloy, orcalcium metal or a calcium-containing alloy may be required to furtheradjust the chemistry of the overall composite to produce aBa-Ca-Al-Si-containing alloy consisting essentially of about 8-13%barium, about 914% calcium, about 17-24% aluminum, about 37-43% siliconand up to 25% of a metal such as iron. An inert gas, such as argon ornitrogen, introduced by a graphite tube from the top, or from a porousplug at the bottom, can be used to stir the alloy for about 3 minutesafter all additions are made, such time period being sufficient tosubstantially homogenize the alloy. Thereafter the alloy, at atemperature between about 1100 C. and about 1250 C., is cast into chillsand allowed to cool to ambient. The alloy is then crushed byconventional techniques and appropriately sized for use.

Not only is the remelting step of the Ca-Ba-Si-containing alloydispensed with, but the formerly wasted superheat of this alloy in itsinitial production is now utilized to aid in the melting and alloying ofthe aluminum and metal additives in the Ba-Ca-Al-Si-containing alloy.

It is also to be understood that aluminum and/or a metal, such as iron,could be preheated in the ladle before the Ca-Ba-Si-containing alloy isfed into the ladle, or

I that aluminum and/or iron could be introduced into the ladle in themolten state after the introduction of the Ca-Ba-Si-containing alloy.Since the reaction of iron with silicon in a silicon-containing alloy isan exothermic reaction and the alloying of aluminum into theCa-Ba-Sicontaining alloy is an endothermic reaction, then the adding ofeach can be varied to maintain the temperature within the ladle at somedesired range.

The single drawing shows a sectional view of a side elevation of aprechill runner for use in implementation of this invention.

In the drawing a submerged arc furnace 1, electrode not shown, has a taphole 11 through which a molten composite 12 of slag 8 andCa-Ba-Si-containing alloy 9 is tapped. Slag 8 is indicated by short linesegments and Ca-Ba-Si-containing alloy 9 is shown as small circles. Thesomewhat intermixed molten composite 12 is tapped onto a downwardlyinclined runner 13 having a straight segment 2 forming an angle Bbetween about 20 and about 60, preferably about 45, with reference tothe horizontal. Segment 3 of runner 13 has a slope A between about andabout 30, preferably about with reference to the horizontal and hasbarriers 4, 5, and 6 projecting upward from its top surface 10. Duringthe initial gravity flow of molten composite 12 upon segment 2 of runner13, the composite 12 cools to a degree whereupon slag 8 becomes moreviscous than alloy 9 and begins to settle to the bottom of composite 12.Upon reaching barrier 4, the portion of slag 8 at the bottom ofcomposite 12 is trapped in cavity 14. The flow of composite 12 is nextinterrupted by barriers 5 and 6, whereupon an additional amount of slag8 is trapped in cavities 15 and 16, respectively. The relativelyslag-free composite 12 accumulates in cavity 17, whereupon thesubstantially pure Ca-Ba-Si-containing alloy, at a temperature betweenabout 1100 C. and'about 1700 C., spills over projection 7 into apreheated ladle 18. At this stage of the process, aluminum, a metal suchas iron, and/or fines of Ca-Ba-Si-containing alloy orCa-Ba-Si-Al-eontaining alloy are added thereto or some elements thereofare in the ladle 18 prior to the introduction of the moltenCa-Ba-Si-containing alloy. An inert gas is introduced through porousplug 19 to stir and homogenize the alloy therein. TheCa-Ba-Al-Si-eontaining alloy is then cast into chills for cooling toambient and thereafter the solidified alloy is crushed into usablesizes. Any Ca-Ba-Si-containing alloy remaining on the runner can beseparated from the slag by conventional techniques and remelted or usedas an additive to adjust the chemistry of the alloy in the ladle.

It should be realized that the runner shown in the drawing is forillustrative purposes and various designs and contour are feasible. Forexample, segment 2 and segment 3 can be disposed with the same slopewithout departing from the invention.

EXAMPLE A 13,000 kilowatt submerged are furnace was used toconventionally produce 5000 lbs. of Ca-Ba-Si-containing alloy which hadslag intermixed therewith. A molded sand runner, similar to the oneshown in the drawing, was positioned adjacent to the tap hole of thefurnace. The horizontal length of the runner was 30 feet with thestraight segment being 12 feet, at a slope of 45, and thebarrier-containing segment being 18 feet, with a slope of 15. The heightof the barrier measured from the lowest point in the cavities was 1.5feet. A 67 cubic foot ladle was positioned at the end of the runner andwas equipped with a graphite tube for introducing nitrogen gas.

Alloy and slag from the furnace were tapped onto the runer andgravity-fed into the ladle. The tapping temperature, weight, andadditions of two heats are shown in Table 1. The molten alloy of thefirst heat was fed into the ladle at a temperature of 1590 C. andvisually indicated no traces of slag. Thereafter 685 lbs. of steel, lbs.of calcium and 1180 lbs. of molten aluminum were introduced whichyielded a final temperature of 1410 C. Nitrogen gas was next introducedthrough a graphite tube in the ladle to stir and homogenize the alloytherein. The stirring continued for 3 minutes after all additions werecompleted and thereafter the alloy was cast into chills measuring 5' x 5x 3" for cooling down to ambient. An analysis of the alloy compositebefore and after the addition of the aluminum, steel and calcium isshown in Table 2.

The same procedure was undertaken for heat 2 except that 250 lbs. ofsteel was in the ladle prior to the introduction of the molten alloyfrom the runner. With the temperature of the steel andCa-Ba-Si-containing alloy in the ladle at 1455 C., an additional 500lbs. of steel, 150 lbs. of calcium, 1390 lbs. of aluminum, and 360 lbs.of Ca-Ba-Si-Al-containing fines were added. This gave a finaltemperature of 1280 C. Nitrogen gas was again introduced to stir thealloy and was continued for 3 minutes after all additions were made. Thealloy was thereafter cast into chills as specified above and an analysisof the alloy is likewise shown in Table 2.

TABLE 1 Tapping temp., 0.) Weight, lbs. Additions, lbs.

From From From From Alloy Heat furnace runner furnace runner Ca Steel Alfines in said ladle to form an aluminum-containing alloy; TABLE 2 andTraces of (g) casting said aluminum-containing alloy. Heat Ca Ba A1 orCr 2. The process of claim 1 wherein at least one of Analysis ofCa-Bg-Si-Gontailling alloy (percent) the additives in step (f) is in theladle prior to introducing the relatively slag-free =Oa-Ba-Si-containingalloy. 1 15.0 16.6 59.8 6.3 1.4 2 16.1 16.0 60.6 5.7 1.6 3. The processof claim 2 wherein at least one of the s v I Analysis ofOa-BrSi-Alcontaining alloy (percent) iives in step (f) 18 added to theladle after the 111110 duction of the relatively slag-freeCa-Ba-Sr-contarmng 1 11-: 18-? 12-; 58-? 61 alloy- 2 4. The process ofclaim 1 wherein at least one of the additives in step (f) is added tothe ladle in the molten 20 state.

What is claimed is:

1. A process for making an aluminum-cointaining alloy addition agentconsisting essentially of about 17-24% aluminum, about 37-43% silicon,about 8-l3% barium, about 9-14% calcium and up to of at least one of themetals selected from a group consisting of iron, nickel, manganese,chromium and cobalt, comprising:

(a) preparing a molten Oa-Ba-Si-containing alloy in a submerged arcfurnace at an elevated temperature wherein slag is intermixed with thealloy;

(b) tapping said slag containing Ca-B'a-Si alloy onto a downwardlyinclined runner, said runner having an initially straight segmentfollowed by a second segment containing at least one barrier projectingupward from the surface into the flow path on said runner so as to forma cavity on said runner;

(c) cooling said slag containing Ca-Ba-Si-alloy to a temperature atwhich the slag becomes more viscous than the Ca-Ba-Si-containing alloywhereupon said slag settles at the bottom of the flow while the alloyrises to the top;

((1) partially obstructing the gravity flow of said slag containingCa-Ba-Si alloy by said barrier so as to trap said slag in the cavityform by said barrier while allowing the alloy .at the upper portion ofthe flow to continue;

(e) collecting said relatively slag-free Ca-Ba-Si-containing alloy in aladle;

(f) mixing said Oa-Ba-Si-containing alloy with an additive consisting ofaluminum and at least one of the metals selected from the groupconsisting of iron, nickel, chromium, calcium, manganese and cobalt 5.The process of claim 1 where the mixing in step (f) is accomplished byintroducing an inert gas into the ladle.

6. The process as in claim 1 wherein in step (b) the slag-containingCa-Ba-Si alloy is tapped at a temperature between about 1500 C. andabout 2100 C.

7. The process as in claim 6 wherein in step (c) the slag-containingCa-Ba-Si alloy is cooled to a temperature between about 1150 C. andabout 1700 C.

8. The process of claim 7 wherein in step (e) the relatively slag-free-Ca-Ba-Si alloy is collected in the ladle at a temperature about 1300 C.

9. The process of claim 1 wherein a calcium-containing alloy is added tothe ladle in step (f) to adjust the chemistry of the aluminum-containingalloy.

References Cited UNITED STATES PATENTS 3,321,300 5/1967 Worner 93 R2,519,593 8/1950 Ofienhaver 26634 PT 1,862,787 6/1932 Error 26638FOREIGN PATENTS 643,325 6/1962 Canada 75-93 R 933,393 8/1963 GreatBritain 75134 WINSTON A. DOUGLAS, Primary Examiner M. J. ANDREWS,Assistant Examiner U.S. Cl. X.R.

75-6'3, 93 R, 134 A, 134 S; 064 134; 266-37, 38

